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| Western bean cutworm may be declining in corn & beans |
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By SHELLY STRAUTZ-SPRINGBORN
Michigan Correspondent
EAST LANSING, Mich. — Western bean cutworm (WBC) continues to threaten corn and dry beans throughout the Great Lakes region and parts of Canada, but researchers are seeing evidence the threat is declining.
“Based on this year’s observations, the overall Western bean cutworm pressure in Michigan may be dropping,” Michigan State University field crops entomologist Chris DiFonzo said.
DiFonzo leads a research project funded by MSU’s Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs) and the state’s corn and dry bean industries. She and her team monitor moth flight timing, egg deposits and larval feeding of the pest throughout the state.
They also cooperate with a group of entomologists around the Great Lakes region, including Canada, which helps them better understand WBC and determine management recommendations for growers.
“The moth flight was lower in sheer numbers this season,” DiFonzo said. “The lower numbers this year hopefully will result in even lower numbers next season.”
In fields this year, she said fewer live larvae are hatching from egg masses than during past years. These larvae can cause severe feeding injury to corn ears and to pods of dry beans, resulting in loss of yield and quality.
“We have observed more biological control than ever, including predation on the egg masses, parasitoids – wasps – emerging from eggs for the first time and insect-killing fungus,” she said.
DiFonzo also said above-average temperatures in July may have reduced egg laying by stressing or killing female moths. As more Bt corn containing the Cry1F trait was planted, there are fewer cornfields that can produce large numbers of larvae. The natural bio-control and Bt hybrids may be “dampening” – or reducing – the population over the landscape.
The decline is also being reported by researchers in Indiana, according to DiFonzo; however, a real “hot spot” is near Bothwell, Ontario, halfway between Detroit, Mich., and London, Ontario.
“This area has sandy soil and is similar to parts of central Michigan where there is also a hot spot,” she said. “In Bothwell this year, entomologists confirmed overwintering of larvae in the soil. After the moths emerged, the flight was huge and thousands of egg masses were collected by Ontario entomologists.”
A spray advisory to safeguard against WBC in dry edible beans was issued on Aug. 1 for several counties in central Michigan because of high trap counts and the known potential risk of the pest to the dry bean crop.
“In research conducted over the past two seasons, we have learned that one well-timed insecticide application can greatly reduce the damage to dry beans from western bean cutworm,” DiFonzo said.
WBC has been present in Michigan for several years. During the 2007 growing season, the northwestern quadrant of the state, from Oceana County to Montcalm County and north, was infested. In 2008, there was significant damage to dry bean crop in a few locations. Most beans in Montcalm County were sprayed in 2009 and 2010, but those left untreated had significant damage.
Historically, WBC was a pest in the Western Corn Belt. It has steadily spread east during the past 10 years, from the high plains of Nebraska and Colorado across the United States. Unlike other cutworms, WBC is a late-season pest. It feeds primarily on corn ears, chewing and scarring kernels, and predisposing the ear to fungus and mold infections.
One generation of WBC occurs each year. Moth emergence usually begins in early July.
Detection is generally more difficult in dry beans than in corn. In corn, the pest is usually eye level, but in beans, scouts basically have to crawl around on the ground to detect it because eggs are laid in area of dense bean foliage on the lower surface of leaves.
Typically, the pest is attracted to fields in which corn is tasseling or near tasseling and fields that have hybrids with upright leaf characteristics. Dry beans are particularly attractive to WBC if neighboring cornfields have already tasseled. Larvae chew holes in pod walls and developing seeds. Most feeding occurs on cloudy days or at night.
If WBC development is not complete, as beans are pulled larvae may congregate under the windrow, feeding on pods and seeds until harvest.
After hatching, larvae feed on host plants for about 31 days. When a larva finishes feeding and completes development, it drops to the ground and burrows into the soil where it overwinters, to begin the cycle again the next year. |
| 8/10/2011 |
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